Redo app loading

[mrerrormessage]

The current application loading code has a splash screen because it takes a while, but (perversely) it also takes a long time because it has a splash screen. A great many of the various calls to pico.add which are currently in org.nlogo.app.App could be moved to a background thread with no loss. If startup was fast enough, we might even be able to ditch the splash screen.

Also, @SethTisue reports that one of the hexy preview builds is opening windows in the background instead of the foreground on his Mac. It seems likely to me that removing the splash screen would resolve this issue.

On my computer the NetLogo app take ~10 seconds on first start and ~3 seconds on subsequent starts to load from double-click to visible frame. That seems too long without a splash screen. The longest amount of time is spent during the initial phase of registering with Pico and initializing App. The second longest is spent loading the default model. I suspect that simplifying the dependencies of various components could reduce that, but I haven't thoroughly profiled startup at this point.